1. Field of the Invention
The present invention relates to a storage system and a storage system management method, and more particularly to a technique whereby, in a storage system that executes hierarchical storage management using stubs, an information inconsistency, between a stub and a file indicated by the stub between layers of a storage apparatus, is efficiently resolved, and whereby the storage system is suitably operated.
2. Description of the Related Art
One method of efficiently utilizing the capacity of a storage system is Hierarchical Storage Management (HSM) in a patent document No. U.S. Pat. No. 7,225,211 B1. An HSM system typically comprises two or more storage apparatuses, namely, a high-speed, low-capacity storage apparatus and a low-speed, high-capacity storage apparatus, which exist in a hierarchical relationship. Each layer in the hierarchy is called a ‘tier’. Furthermore, the high-speed, low-capacity storage layer is called a ‘higher tier’, while the low-speed, high-capacity storage layer is called a ‘lower tier’. In HSM, data is first stored in the higher tier, and data with a low usage frequency is moved (migrated) to the lower tier, thus making efficient use of storage capacity.
Stubs are often used to allow the data moved to the lower tier to be referred to easily. Stubs are disposed in the higher tier and indicate storage locations in the lower tier to which the data has been moved. A user is able to refer to the data moved to the lower tier by referring to the stub in the higher tier. In an HSM that uses such stubs, information inconsistency between stubs that exist in the higher tier and the data of files and so on present in the lower tier indicated by the stubs are sometimes a problem. Here, a mismatch refers to a case where a stub in the higher tier does not indicate a suitable lower tier file, or a case where a stub that should indicate a lower tier file does not exist in the higher tier.
Another patent document U.S. Pat. No. 6,023,709 B1 discloses a technique whereby, when receiving access that requires a stub to be referenced, a higher-tier storage apparatus notifies an access source of an error when a stub mismatch is detected, and then executes error repair.
The mismatch mentioned above may often arise in cases where a restore from backup data in the higher tier is executed or where a file is deleted in the lower tier, for example.
In a method disclosed in patent document U.S. Pat. No. 6,023,709 B1, an error in data indicated by a stub is detected and repaired at the point where a user accesses the stub. This method therefore fails to address a case where the stub itself is lost. Moreover, since the method described in the above patent document does not allow an inconsistency to be dealt with until the user performs access, this is an inconvenience to the user.